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The Alxa area in Inner Mongolia has been selected as a possible site for geological disposal of high-level radioactive waste (HLRW). Based on results of a previous study on crustal stability, the Tamusu rock mass has been chosen as the target. To determine the geological structure of this rock mass, aeromagnetic and gravity data are collected and inverted. Three-dimensional (3D) inversion horizontal slices show that the internal density of the rock mass and the distribution of magnetic properties are not uniform, with fractures and fragmentation being present. To confirm this result, the controlled source audio-frequency magnetotelluric method (CSAMT) was applied to explore the geological structures, the typical CSAMT sounding curve was analyzed, and the response characteristics of the geological structure and surrounding rock are distinguished. The original data were processed and interpreted in combination with data from surface geology and drilling and logging data. It is found that the CSAMT results were consistent with those from 3D inversion of the gravity and magnetic data, confirming the existence of fractures and fragmentation in the exploration area. [ABSTRACT FROM AUTHOR]

Dense array Magnetotelluric sounding (MT) was applied in the study of the emergence of massive gold deposits relating to the tectonic activity responsible for the creation of the North China Craton. This study focuses on understanding the shallow crustal electrical structure characteristics (>1.5 km) of Pb Zn and Au Ag deposits in the Qingchengzi orefield, through the analysis of shallow electrical resistivity distribution at depths less than 5 km, obtained by 3D inversion of full impedance at a frequency range of 320–0.107 Hz. The results showed that the electrical characteristics of Xiaotongjiapuzi and Taoyuan deposits in the 3D resistivity model are consistent with the known 2D resistivity model, and the Jianshanzi fault plays an important role in the gold mineralization, acting as a migration channel and precipitation zone for ore-forming materials. It is inferred that the fault extends at least 5 km deep with deep mineralization prospects. The strata of Liaohe Group in the north of the orefield, the intrusive granite in the south, and the NW-trending Jianshanzi and Yushanggou faults show distinguishable electrical properties, which are either high resistance, low resistance, or high and low resistance transition zone on the depth slice map. Furthermore, the Xinling rock mass has a NE trending extension, which confirms the inference that the Jianshanzi fault extends to a depth of 5 km into the crust. • Imaging shallow crustal electrical structures through 3D inversion of MT data. • Relationship of mineralization with the electrical structure, fault, and lithology. • Guide the deep prospecting direction of polymetallic deposits in the future. [ABSTRACT FROM AUTHOR]